The present invention relates to a circuit for processing communication data such as packets or cells, and more particularly to a communication data processing circuit realizing low power consumption.
In the recent Internet environment, the problems of power costs and global warming due to increased electric power and due to continuous energizing of respective apparatuses have been pointed out with the advance of conversion to broadband and to always-on connection.
In general access-system communication lines, the actual time period during which packets are transmitted is very short. Usually, most of the transmission time period is not used to transmit packets. However, the conventional packet processing circuit wastefully consumes the electric power because the clock signal is always in an on state, regardless of the presence or absence of packet transmission.
As to the technique of aiming at low power consumption of a packet processing circuit, JP-P1999-116131A, for example, discloses the processing circuit that makes clocks therefor in an on state by a predetermined period from a packet inputting time to suppress the power consumption.
In another technique, JP-P2000-77983A discloses the circuit that validates a clock signal only when data changes with a gate signal applied to the clock port for a flip-flop in word units of data, so that power consumption is suppressed.
Of the above-mentioned related circuits, the packet processing circuit, in which the packet length varies largely, disclosed in JP-P1999-116131A requires setting the time period the clock to an ON state based on a packet with a maximum packet length. For that reason, the packet processing circuit has the disadvantage that low power consumption cannot be effectively accomplished to shorter packets.
Moreover, the circuit disclosed in JP-P2001-177382A applies a gate signal to the clock port of the flip-flop in data word units and validates the clock only when data changes. For that reason, there is the disadvantage that the unit for gating is segmentized and the control circuit is complicated and increased in number.